Disease

[ZIC3_HUMAN] Defects in ZIC3 are the cause of visceral heterotaxy X-linked type 1 (HTX1) [MIM:306955]. A form of visceral heterotaxy, a complex disorder due to disruption of the normal left-right asymmetry of the thoracoabdominal organs. It results in an abnormal arrangement of visceral organs, and a wide variety of congenital defects. Clinical features of visceral heterotaxy X-linked type 1 include dextrocardia, corrected transposition of great arteries, ventricular septal defect, patent ductus arteriosus, pulmonic stenosis, situs inversus viscerum, and asplenia and/or polysplenia.[1][2][3][4][5] Defects in ZIC3 are a cause of VACTERL association X-linked with or without hydrocephalus (VACTERLX) [MIM:314390]. A syndrome characterized by vertebral anomalies, anal atresia, cardiac malformations, tracheoesophageal fistula, renal anomalies (urethral atresia with hydronephrosis), and limb anomalies (hexadactyly, humeral hypoplasia, radial aplasia, and proximally placed thumb). Some patients may have hydrocephalus. Some cases of VACTERL-H are associated with increased chromosome breakage and rearrangement.[6] Defects in ZIC3 are the cause of congenital heart defects, multiple types, 1, X-linked (CHTD1) [MIM:306955]. A disorder characterized by congenital developmental abnormalities involving structures of the heart. Common defects include transposition of the great arteries, aortic stenosis, atrial septal defect, ventricular septal defect, pulmonic stenosis, and patent ductus arteriosus. The etiology of CHTD is complex, with contributions from environmental exposure, chromosomal abnormalities, and gene defects. Some patients with CHTD1 also have cardiac arrhythmias, which may be due to the anatomic defect itself or to surgical interventions.[7][8]

Function

[ZIC3_HUMAN] Acts as transcriptional activator. Required in the earliest stages in both axial midline development and left-right (LR) asymmetry specification. Binds to the minimal GLI-consensus sequence 5'-GGGTGGTC-3'.[9]

Evolutionary Conservation

Publication Abstract from PubMed

Disruptions in ZIC3 cause heterotaxy, a congenital anomaly of the left-right axis. ZIC3 encodes a nuclear protein with a zinc finger (ZF) domain that contains five tandem C2H2 ZF motifs. Missense mutations in the first ZF motif (ZF1) result in defective nuclear localization, which may underlie the pathogenesis of heterotaxy. Here we revealed the structural and functional basis of the nuclear localization signal (NLS) of ZIC3 and investigated its relationship to the defect caused by ZF1 mutation. The ZIC3 NLS was located in the ZF2 and ZF3 regions, rather than ZF1. Several basic residues interspersed throughout these regions were responsible for the nuclear localization, but R320, K337 and R350 were particularly important. NMR structure analysis revealed that ZF1-4 had a similar structure to GLI ZF, and the basic side chains of the NLS clustered together in two regions on the protein surface, similar to classical bipartite NLSs. Among the residues for the ZF1 mutations, C253 and H286 were positioned for the metal chelation, whereas W255 was positioned in the hydrophobic core formed by ZF1 and ZF2. Tryptophan 255 was a highly conserved inter-finger connector and formed part of a structural motif (tandem CXW-C-H-H) that is shared with GLI, Glis and some fungal ZF proteins. Furthermore, we found that knockdown of Karyopherin alpha1/alpha6 impaired ZIC3 nuclear localization, and physical interactions between the NLS and the nuclear import adapter proteins were disturbed by mutations in the NLS but not by W255G. These results indicate that ZIC3 is imported into the cell nucleus by the Karyopherin (Importin) system and that the impaired nuclear localization by the ZF1 mutation is not due to a direct influence on the NLS.